Problem: If $6a + 8b + 4c = -6$ and $3x + 3y = 7$, what is $-3y - 42a - 3x - 28c - 56b$ ?
Solution: $= -42a - 56b - 28c - 3x - 3y$ $= (-7) \cdot (6a + 8b + 4c) + (-1) \cdot (3x + 3y)$ $= (-7) \cdot (-6) + (-1) \cdot (7)$ $= 42 - 7$ $= 35$